Electric control for hydraulic lifts



Dec. 13, 1955 P. w. ROHRBERG ELECTRIC CONTROL HYDRAULIC LIFTS 2 Sheets-Sheet 1 Filed Feb. 25, 1955 lll ll INVENTOR Paul Rohrberg BY lfi ATTORNEYS Dec. 13, 1955 P. w. ROHRBERG ELECTRIC CONTROL HYDRAULIC LIFTS 2 Sheets-Sheet 2 Filed Feb. 23, 1955 ATTORNEYS United States Patent D ELECTRIC CONTROL FOR HYDRAULIC LIFTS Paul W. Rohrberg, Watertown, N. Y., assignor to The New York Air Brake Company, a corporation of New Jersey Application February 23, 1955, Serial No. 489,901

5 Claims. (Cl. 187-29) This invention relates to hydraulic lifts, and more par- .ticularly to a combined electrical-hydraulic control system for such lifts.

There is a current demand for hydraulic lifts for use in parking garages and parking lots for selectively raising cars to a level which enables other cars to be parked thereunder. The use of such equipment greatly increases the number of cars which can be parked in a given area and thus increases the possible revenue from parking operations when figured on a square foot basis.

It is the principal object of this invention to provide a simplified electrical control system for the operation of such lifts which embodies a number of safety features which inhibit faulty operation, and render the lift safe for operating personnel. Other objects will be apparent from the following description, read in conjunction with the attached sheets of drawing, in which:

Figure l is a schematic representation of the basic electrical and hydraulic controls, and

Figure 2 is a schematic wiring diagram for a two-car lift.

Basically, the hydraulic system includes a motor-driven pump and liquid storage tank connected by valves to a double-acting piston motor which raises and lowers a platform upon which a car may be parked. In addition, the hydraulic system is of the type (not the invention of this applicant) which hydraulically locks itself at any intermediate position between the upper and lower limits of travel and requires the application of fluid under pressure to move the piston and connected platform in either upward or downward directions. As an added safety feature, a mechanical latch is provided which is normally biased to a position beneath the platform when the latter is in its raised position, so that leakage in the hydraulic system, while a car is on the lift in raised position, cannot result in inadvertent lowering.

Referring now to Figure 1 of the attached drawings, the pump 10, its associated driving motor 11, the storage tank 12, and the valve 13, are shown in the upper righthand portion of this figure. The platform 14, the cylinder 15 with piston 16, and also the latch 17, are shown in the lower portion of Figure 1. The latch 17 is normally biased to a position beneath the platform by the spring 18, shown immediately to the left of the latch member.

In the interests of a simplified disclosure, Figure 1 shows only the electrical and hydraulic circuits for a single platform lift. It will be understood that some of the controls in actual practice are duplicated so that a single installation serves a double platform lift.

The valve 13 is of a type which is normally biased to an unloading position in which it recirculates fluid from the high pressure side of the pump back to the low pressure side. It may be moved to either one of two other positions, one of which causes fluid from the high pressure side of the pump to flow to the underside of the piston to raise the platform. In its other position, the valve causes fluid to flow to the upper side of the piston to IC&

lower the platform. In accordance with the invention, this valve is electrically operated by a pair of solenoids 19 and 20 which are basically under the direct control of a pair of push button switches 21 and 22. In addition, however, the basic control between the up and down push-button switches and the valve solenoids is modified by the operation of limit switches controlled by movement of the platform. The first of these switches 23 is positioned to stop the rise of the platform as it arrives in parking position. The contacts are normally closed, and connected between the up solenoid 19 and the up push-button 21 so that the valve is automatically returned to its neutral or unloading position when the platform reaches the raised position shown in the draw ing. A similar limit switch 24 is connected between the down solenoid 20 and the down push-button 22, to return the valve 13 automatically to its unloading position when the platform reaches its lower limit of travel, irrespective of continued application of pressure to the down" push-button switch. Another solenoid 25 which appears in the upper left-hand portion of Figure 1 controls the application of power to the motor 11 which drives the pump 10. The three-contact switch 26 associated with this solenoid is normally open, but is closed whenever solenoid 25 is energized by the actuation of either the up or down push-button switch.

The system as thus far described would be suflicient to permit push-button raising and lowering of the platform with an automatic cut-off adjacent either end of the platform path of travel. In order, however, to prevent accidental lowering of the platform in the event that leakage should develop at some point in the hydraulic system, a mechanical latch is provided. The latch member 17 is spring biased to normally underlie the platform in its raised position. The bevelled edge portion 27 permits mechanical retraction of the latch by the platform in its upward movement so that when the platform has been raised, the latch will automatically assume the position indicated on the drawing. A solenoid 28 is provided to retract the latch member to allow the platform to be lowered in response to manual actuation of the down push-button switch. However, the latch member may be frictionally restrained by the weight of the platform and its load sufficiently to preclude its retraction by the solenoid 25 unless the platform is first raised slightly, to free the latch member. To achieve lowering of the platform, therefore, it is necessary first to raise it slightly, and the switches which control this operation further modify the direct control between the push-button switches and the valve solenoids.

The first of two limit switches which control this operation is shown at 29 and includes one movable and two fixed contacts 30, and 31 and 32. The movable contact is normally in engagement with the lower fixed contact 32. When the platform is in its raised and latched position, the movable contact 30 engages the upper fixed contact 31. When this switch is in the position shown in Figure l, actuation of the down push-button switch 22 energizes the up rather than the down, valve-actuating solenoid so that the platform begins to rise. Still another limit switch 33 has normally open contacts positioned to be ciosed by upward movement of the platform from its latched position. When this switch is closed, control solenoid 34 is energized. This control solenoid 34 has a pair of normally open, and a pair of normally closed, contacts 35 and 36. The purpose of solenoid 34 is to modify the connections between valve solenoids 19 and 2t) and the push buttons 21 and 22 so that the up valve actuating solenoid 19 is locked out of the circuit in favor of the down valve actuating solenoid 20, when solenoid 34 is energized.

Actuation of the limit switch 33 in addition to energizing the control solenoid 34, also energizes the solenoid 28 which retracts the safety latch. Downward movement of the platform from this raised position, allows movable contact 30 of limit switch 29 to engage the lower fixed contact 32. This modification establishes a parallel holding circuit through the down valve actuating solenoid 2t) and through limit switch 24 and serves as a means for continuing down operation in the event of a failure of the coil of solenoid 34. The basic holding circuit is through contact 35, which is closed when solenoid 34 is energized. The platform is thus allowed to move down past the latch, and its downward movement will continue until the down push-button is released or until the lower limit switch is actuated by reason of the platform arriving at its lower limit of travel.

Referring now to Figure 2, there is shown the entire schematic wiring diagram for a unit control system for a double platform lift. Reference characters which apply to the same elements shown in Figure 1 are duplicated, and those which apply to the other half of the circuit, not shown in Figure l, are given the corresponding reference numerals with the letter A appended thereto.

An additional safety feature includes the switch 37.

This switch may be key-operated by the parking lot attendant and serves to isolate one and energize the other of the lift-control circuits. This insures that only one of each lift pair may be operated at any given time. Still another safety feature includes an alarm bell 33 which is operated whenever either the up or down push button switch is depressed, thus sounding an audible warning signal to anyone in the area that the lift is in motion.

The operation of the device for a complete raising and lowering cycle is as follows: Assume that the platform 14 is in its fully lowered position, that a car has been driven onto the platform and that it is desired to raise the platform to a point to enable another car to be parked beneath the platform. Referring first to Figure 2, the key selector-switch 37 must first be moved from its locked off position to one or the other of its two on positions in order that power may be applied to a selected control circuit. Until this switch is moved from its neutral or off position, it is not possible to energize either control circuit. With the key selector switch in one of its two on positions, actuation of the down push-button switch 22 will have no effect because the circuit to the down valve-actuating solenoid is broken at the limit switch 24 by reason of the platform being in its fully lowered position. Pressing the up pushbutton switch 21, however, energizes solenoid 25 which closes switch 26 to start the motor 11. Simultaneously, the alarm hell 3%? sounds and valve actuating solenoid 19 is energized to move the valve 13 to a position which allows fiuid to flow from the high pressure side of the pump 10 to the underside of the piston 16 in the cylinder 15. The platform begins to rise and continues to do so until limit switch 23 is opened, which removes power from solenoid 19 and allows the valve 13 to return to its neutral or unloading position. At this point, the platform has risen far enough to clear the latch 17 which thereupon automatically assumes the position shown in Figure l. The up push-button may now be released and the platform will remain in its raised position shown in Figure 1, with no further application of electrical power to the control circuit.

The lowering of the platform from its raised latched position will now be described: The up push-button is now electrically isolated from the control circuit due to the opened condition of limit switch 23. It is, however, necessary to effect a further raising of the platform in order that latch 17 may be retracted. This additional raising is accomplished automatically when the down push-button is pressed. Contacts 30 and 31 of limit switch 29 were also closed by movement of the platform to the position shown in Figure l and, therefore, actuation of the down push-button switch 22 establishes a circuit from one side of the line through contacts 30 and 31, normally closed contacts 36 of solenoid 34, the up valve actuating solenoid l9, and back to the other side of the line. This moves valve 13 to platform-raising position. The platform starts to rise, but continues to do so only until limit switch 33 is closed by this upward movement. As the platform descends, and before limit switch 33 is reopened, the normally closed contacts 30 and 32 of limit switch 29 close to establish the secondary holding circuit for latch solenoid 28, which is complete as long as the down push-button switch 22 is held. The first of these energizes the control solenoid 34, which opens its contacts 36 and closes its contacts 35. Opening of contacts 36 removes power from the up valve-actuating solenoid 19. Closing of contacts 35 applies power to the down valveactuating solenoid 20 to shift the valve 13 to a position to apply fluid pressure to the upper side of piston 16 in cylinder 15. Accordingly, the platform now begins to descend. The second circuit completed by the closing of limit switch 33 is one between the latch solenoid 28 and the power source, so that the latch 17 is retracted. As the platform descends, and before limit-switch 33 is re-opened, normally-closed contacts 30 and 32 of limit switch 29 close to establish a holding circuit for the latch solenoid 28, which is complete as long as the down push-button switch 22 is held. The platform continues to descend, therefore, until push-button switch 22 is released or until limit switch 24 is opened by the platform when it arrives at its fully lowered position.

It should be noted that the key selector switch 37 must be moved to its other position before power can be applied to the circuits for controlling the other associated lift. Thus, although a single set of up" and down push-buttons controls both lift control circuits, it is impossible for more than one hoist to be operated at the same time.

From the foregoing it will be apparent to those skilled in the art that there is herein shown and described a novel and useful control circuit arrangement for hydraulic lifts. While the invention has been described primarily with reference to automobile parking devices, the basic invention is applicable to the control of hydraulic lifts generally.

What is claimed is:

l. A combined hydraulic electrical control system for a hydraulic platform lift of the type which is positively raised and lowered, comprising: a source of fluid pressure; a cylinder-enclosed piston connected to the platform; a safety latch member normally biased to a position beneath the platform in its raised position; means including electrically-operated valve means for feeding fluid from said pressure source selectively to either side of said piston; manually-operated switch means for selectively controlling said valve means; a solenoid operative when energized to retract the safety latch from the platform path of travel; a first limit switch positioned adjacent the raised position of the platform and actuated by the platform for energizing the latch solenoid; a second limit switch positioned adjacent the raised position of the platform, actuated by the platform, and operative when actuated so to modify the connections between the manual switch and the valve that when the platform is in its raised latched position, actuation of the manual switch to lower the platform results in an initial upward movement to mechanically unload the latch and close the first limit switch to retract the latch.

2. A combined hydraulic electrical control system for a hydraulic platform lift of the type which is positively raised and lowered, comprising: a source of fluid pressure; a cylinder-enclosed piston connected to the platform; a safety latch member normally biased to a position beneath the platform in its raised position; means including electrically-operated valve means for feeding fluid from said pressure source selectively to either side of said piston; manually-operated switch means for selectively controlling said valve means; first and second limit switches positioned adjacent the raised and lowered positions of the platform and actuated by the platform for automatically deenergizing the electrically-operated valves; a solenoid operative when energized to retract the safety latch from the platform path of travel; a third limit switch positioned adjacent the raised position of the platform and actuated by the platform for energizing the latch solenoid; a fourth limit switch positioned adjacent the raised position of the platform, actuated by the platform, and operative when actuated so to modify the connections between the manual switch and the valve so that when the platform is in its raised latched position, actuation of the manual switch to lower the platform results in an initial upward movement to mechanically unload the latch and close the third limit switch to retract the latch.

3. In a fluid pressure operated lift of the type which includes a movable platform, a cylinder having a piston therein connected to move said platform, a source of fluid pressure, means including valve means for controlling the admission of fluid from said source to either side of said piston, and latch means to mechanically lock the platform in raised position, an electrical control circuit comprising: first solenoid means operative when energized to move the valve to admit fluid pressure selectively to either side of the piston to raise or lower the platform; first normally open switch means connected to said solenoid means and to a source of electrical energy; second solenoid means for moving the latch from operative to inoperative position; second normally open switch means connected between the latch solenoid and the source of electrical energy, and positioned to be closed by movement of the platform above the latch; and further switch means positioned to be operated by the platform adjacent its upper limit of travel, said means being electrically connected to and serving to over-ride said first switch means so that when said platform is in its upper latched position and said first switch means is closed to lower the platform, the platform first rises to mechanically unload the latch and closes the second normally open switch means to retract the latch, then closes said further switch means to energize the first solenoid to move the valve to platform lowering position.

4. A combined hydraulic electrical control system for a hydraulic platform lift of the type which is positively raised and lowered, comprising: a source of fluid pressure; a cylinder-enclosed piston for raising and lowering the platform; means including a valve connecting the pressure source to opposite sides of the piston; a latch member normally biased into the downward path of platform travel when the latter is in its raised position; first and second solenoids, each operative when energized to move the valve to one of two positions corresponding to platform raising or lowering; normally open switch means connected to said solenoids and affording selective energization of the said solenoids; a first limit switch having normally closed contacts connected in series with the raising solenoid, said switch being positioned to be opened by upward movement of the platform to a position which allows the latch to lock the platform in raised position; a third solenoid operative when energized to move the latch to inoperative position; a second limit switch having normally opened contacts connected in circuit with said second solenoid and operative when closed to energize said second solenoid to retract the latch, said switch being positioned to be closed by upward movement of the platform from its raised locked position; a solenoid relay having a pair of normally open and a pair of normally closed contacts; a third limit switch having a pair of normally open and a pair of normally closed contacts, said switch being positioned to be opened and closed by upward movement of the platform to its raised position and to be closed and opened by downward movement of the platform from its raised and latched position, said normally open contacts being connected in series with said platform raising solenoid and said normally closed contacts being connected in series with said solenoid relay; and a fourth limit switch having normally closed contacts connected in series with the lowering solenoid and positioned to be opened by downward movement of said platform at the lower limit of its downward travel.

5. A system as defined in claim 1, in which an audible alarm is connected to be energized by said manuallyoperated switch means.

No references cited. 

